HGH-RH(1-29)NH2 analogues having antagonistic activity

ABSTRACT

A peptide selected from the group having the formulae: 
     α) X-R 1  -R 2  -R 3  -R 4  -R 5  -R 6  -Thr-R 8  -R 9  -R 10  -R 11  -R 12  -Val-Leu-R 15  -Gln-Leu-Ser-R 19  -R 20  -R 21  -Leu-Leu-Gln-Asp-Ile-R 27  -R 28  -R 29 , wherein X is H, Ac, Aqc, IAc, BrProp, For, Ibu, Nac, 2-Nac, 1- or 2-Npt, 1- or 2-Npr, PhAc, Fpr, or any other aromatic or nonpolar acyl group, R 1  is Tyr, His or Phe(Y), in which Y=H, F, Cl, Br, NO 2 , CH 3  or OCH 3 , R 2  is D-Arg, D-Cit, D-Har, D-Lys, D-Tic or D-Orn, R 3  is Asp, D-Asp, Ala, D-Ala or Gly, R 4  is Ala, Abu or Gly, R 5  is Ile, Ala or Gly, R 6  is Phe, Tic, Ala, Pro, Tpi, Nal or Phe(Y), in which Y=H, F, Cl, Br, NO 2 , NH 2 , CH 3  or OCH 3 , R 8  is Asn, Gln, Ser, Thr, Val, Leu, Ile, Ala, D-Ala, D-Asn, D-Gln, D-Thr, D-Leu, Abu, D-Abu, Nle, or Alb, R 9  is Ser, R 10  is Tyr or Phe(Y), in which Y=H, F, Cl, Br, NO 2 , CH 3  or OCH 3 , R 11  is Arg, D-Arg, or Cit, R 12  is Lys, D-Lys, Cit, D-Cit, Orn, D-Orn, Nle or Ala, R 15  is Gly, Ala, Abu or Gln, R 19  is Ala or Abu, R 20  is Arg, D-Arg or Cit, R 21  is Lys, D-Lys, Orn or Cit, R 27  is Met, Nle or Abu, R 28  is Ser, Asn, Ala or Abu, R 29  is Agm, Arg-NH 2 , Arg-OH, Cit-NH 2 , Cit-OH, Har-NH 2  or Har-OH, and 
     β) X-A 1  -B 2  -A 3  -R 4  -R 5  -R 6  -Thr-A 8  Ser-R 10  -R 11  -B 12  -Val-Leu-R 15  -A 16  -A 17  -Ser-R 19  -B 20  -B 21  -Leu-Leu-Gln-A 26  -Ile-R 27  -R 28  -R 29 , wherein a lactam bridge is formed between any one of the pairs of positions 1,2; 2,3; 8,12; 16,20; 17-21; 21,25; 25,29 or both 8,12 and 21,25 positions, and X is H, Ac, Aqc, IAc, BrProp, For, Ibu, Nac, 2-Nac, 1- or 2-Npt, 1- or 2-Npr, PhAc, Fpr, or any other aromatic or nonpolar acyl group, A is Glu, D-Glu, Gln, Asp, D-Asp, Asn, Abu, Leu, Tyr, His, Phe(Y), in which Y=H, F, cl, Br, NO 2 , NH 2 , CH 3  or OCH 3 , Ser, Thr, Val, Ile, Ala, D-Ala, D-Asn, D-Gln, D-Thr, D-Leu, Abu, D-Abu, Nle, or Aib, B is Lys, D-Lys, Arg, D-Arg,Orn, D-Orn, or Agm; R 4  is Ala, Abu or Gly, R 5  is Ile, Ala or Gly, R 6  is Phe, Tic, Tpi, Nal or Phe(Y), in which Y=H, F, Cl, Br, NO 2 , NH 2  CH 3  or OCH 3 , R 10  is Tyr or Phe(Y), in which Y=H, F, Cl, Br, NO 2 , NH 2  CH 3  or OCH 3 , R 15  is Gly, Ala, Abu or Gin, R 27  is Met, Nle or Abu, R 28  is Ser, Asn, Asp, Ala or Abu, and pharmaceutically acceptable salts thereof.

FIELD OF INVENTION

This invention was made in part with Government support from the Medical Research Service of the Veterans Affairs Department. The Government has certain rights in this application.

The present invention relates to novel synthetic peptides which inhibit the release of growth hormone from the pituitary in mammals, and to therapeutic compositions containing these novel peptides.

BACKGROUND OF THE INVENTION

Growth Hormone ("GH") is a peptide having 191 amino acids which stimulates the production of numerous different growth factors, e.g. IGF-I and so promotes growth of numerous tissues (skeleton, connective tissue, muscle and viscera) and physiological activities (raising nucleic acid and protein synthesis and lipolysis, but lowering urea secretion).

Release of GH is under the control of releasing and inhibiting factors secreted by the hypothalamus. The primary releasing factor is growth hormone releasing hormone ("GH-RH"); human growth hormone-releasing hormone ("hGH-RH") is a peptide having 44 amino acids. The novel peptides of the present invention relate to analogues of hGH-RH having only residues 1 through 29 ("hGH-RH(1-29)NH₂ "), i.e., to analogues of the peptide which has the amino acid sequence:

Tyr-Ala-Asp-Ala-Ile⁵ -Phe-Thr-Asn-Ser-Tyr¹⁰ -Arg-Lys-Val-Leu-Gly¹⁵ -Gln-Leu-Ser-Ala-Arg²⁰ -Lys-Leu-Leu-Gln-Asp²⁵ -Ile-Met-Ser-Arg²⁹ -NH₂

GH has been implicated in several diseases. One disease in which GH is involved is acromegaly, in which excessive levels of GH are present. The abnormally enlarged facial and extremity bones of this disease can be treated by administering a GH-RH antagonist.

Further diseases involving GH are diabetic retinopathy and diabetic nephropathy. The damage to the retina and kidneys respectively in these diseases, believed to be due to GH, results in blindness or reduction in kidney function. This damage however can be prevented or slowed by administration of an effective GH-RH antagonist.

In an effort to intervene in these disease and other conditions, some investigators have attempted to control GH levels by using somatostatin, one inhibitor of GH release. However, somatostatin, if administered alone, does not suppress GH or IGF-I levels to a desired degree. If administered in combination with a GH-RH antagonist, somatostatin would improve suppression of IGF-I levels much better.

Other workers have investigated various modifications of GH-RH to elucidate the relationship of the structure of GH-RH to its activity in an effort to provide synthetic congeners with improved agonistic or antagonistic properties. (Synthesis may be by solid phase method, described in U.S. Pat. No. 4,914,189, or in liquid phase, as described in U.S. Pat. No. 4,707,541.) Thus, in one study, it was found that synthesizing GH-RH without its N-terminus residue--i.e., forming hGH-RH(2-44)--results in an analogue having GH releasing activity which is only 0.1% that of GH-RH. By contrast, synthesizing a GH-RH analogue without its residues 30 through 44--i.e., synthesizing hGH-RH(1-29)NH₂ --results in an analogue which retains 50% or more of the potency of native hGH-RH. Synthesizing even shorter analogues--e.g., GH-RH(1-28)NH₂ or GH-RH(1-27)NH₂ --resulted in substantially lower bioactivity. These results indicate that sequence 1-29 is important to the bioactivity of GH-RH.

In another study, it was found that acetylating the N-terminus amino acid residue of GH-RH or replacing it with a D-isomer--thus forming Ac-Tyr¹ !GH-RH or D-Tyr¹ !GH-RH--lowers the ability of the analogues to release GH to 2-3% that of GH-RH. These analogues also have less affinity in vitro for GH-RH binding sites. By contrast, acetylation of the alpha amino group of residue 1 in hGH-RH(1-29)NH₂ --thus forming AcTyr¹ !hGH-RH(1-29)NH₂ --is found to raise the in vivo potency over that of GH-RH by ten fold or more.

In further studies, it was found that Ac-Tyr¹,D-Arg² !hGH-RH(1-29) NH₂ antagonizes the activation of rat anterior pituitary adenylate cyclase by hGH-RH(1-29)NH₂. The same peptide was found to block the action of GH-RH on its receptors in the pituitary and hypothalamus, and to inhibit the pulsatile growth hormone secretion.

Several reported modifications to GH-RH have resulted in agonistic activity. U.S. Pat. No. 4,659,693 discloses agonists of hGH-RH(1-29) having the formula:

R¹ -R² -Asp-Ala-Ile-Phe-Thr-Asn-Ser-Tyr-Arg-Lys-Val-Leu-Gly-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-R²⁷ -Ser-Arg-NH₂,

wherein R¹ is H, Tyr or His; R² may be various residues; and R²⁷ is Nle. These agonists are said to stimulate release of growth hormone releasing factor ("GRF") and so to be suitable in pharmaceutical compositions. ("GRF" is merely a synonym for GH-RH, and the latter abbreviation is used hereinafter, despite use of GRF in U.S. Pat. No. 4,659,693 and other publications.)

U.S. Pat. No. 4,914,189 discloses other analogues of GH-RH which are agonists. In these agonists, the N-terminus group Q¹ CO--, where Q¹ signifies certain omega or alpha-omega substituted alkyl groups, may be Tyr or des-amino-Tyr; the C-terminus group NH-Q², where Q² signifies certain lower omega-guanidino-alkyl groups, may be Agm; and R²⁷ may be Nle. These analogues are said to be extremely potent stimulants of GH release and to enjoy high resistance to in vivo enzymatic degradation due to the omega-guanidino-lower alkyl group at the C-terminus.

Published application WO 91/16923 reviews earlier attempts to alter the secondary structure of hGH-RH by modifying its amino acid sequence. These earlier attempts include: replacing Tyr¹, Ala², ASp³ or Asn⁸ with their D-isomers; replacing Ser⁹ with Ala to enhance amphilicity of the region; and replacing Asn⁸ with L- or D-Ser, D-Arg, Asn, Thr, Gln or D-Lys. Certain of these modifications are said to enhance GH releasing activity. WO 91/16923 also states that replacing Asn⁸ with Ala induces an enormous increase in GH releasing activity. The peptides said to have this benefit have the formula:

R¹,R²,Ala⁸,R¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂,

where R¹ is Dat or A-R¹, where A is lower acyl or benzyl and R¹ includes Tyr and His; R² is Ala, D-Ala or N-Me-D-Ala (N-Methyl-D-Ala); and R¹⁵ may include Gly, Ala or Aib. One preferred embodiment has R⁸,9,15 as Ala. It is noted that R⁸ in this publication is never Asn. Pharmaceutical compositions for enhancing growth are further disclosed.

European Patent Application Ser. No. 0 413 839 A, filed Aug. 22, 1989, assigned to the same assignee as the present application, discloses analogues of hGH-RH(1-29)-NH₂ said to have enhanced release of GH. The 29 as follows: R¹ may be Tyr or Dat; R² may be L or D Ala; R⁸ may be Asn or Ser; R¹² may be L or D isomers of Lys, Arg or Orn; R¹⁵ may be Gly or Ala; R²⁷ may be NIe; R²⁸ may be Asp, Asn or Ser; and R²⁹ may be Agm. However, residue 6 is never replaced: it is always Phe.

Yet another modification of hGH-RH was disclosed in U.S. Pat. No. 5,183,660, where GH-RH was conjugated with polyethylene glycol derivatives. The resulting conjugate was said to exhibit decreased antigenicity, delay in biological clearance in vivo and physiological activity over a longer time.

In several of these investigations, it was found that variants of the hGH-RH agonistic analogues had antagonistic, rather than agonistic, activity. Thus, in U.S. Pat. No. 4,659,693 (where R² may be certain D-Arg residues substituted with alkyl groups), when R¹ is H, the hGH-RH analogues are said to act as antagonists. Similarly, in WO 91/16923, discussed above, if R² in the analogues is D-Arg, and R⁸, R⁹, and R¹⁵ are substituted as indicated above, antagonistic activity is said to result. These antagonistic peptides are said to be suitable for administration as pharmaceutical compositions to treat conditions associated with excessive levels of GH, e.g., acromegaly.

The antagonistic activity of the hGH-RH analogue " Ser⁹ -ψ CH₂ --NH!-Tyrl!hGH-RH(1-29)" of U.S. Pat. No. 5,084,555 was said to result from the pseudopeptide bond (i.e., a peptide bond reduced to a CH₂ --NH! linkage) between the R⁹ and R¹⁰ residues. (It is noted that although this patent employed the seemingly redundant "ψ CH₂ --NH!" formula for the pseudo-peptide bond, actually only one such linkage had been introduced into the peptide.) However, the antagonistic properties of Ser⁹ -ψ CH2--NH!-Tyr¹⁰ !hGH-RH(1-29) were said to be inferior to a conventional antagonist, N-Ac-Tyr¹, D-Arg² !GH-RH(1-29)-NH₂.

U.S. Pat. No. 5,084,442 discloses cyclic lactam analogues of GH-RH which are agonists. The introduction of lactam bridge into peptides or proteins is known to reduce the number of possible conformations. Incorporation of constraints into biologically active peptides may improve receptor binding and result in analogs which have enhanced or prolonged biological activity.

SUMMARY OF THE INVENTION

There is provided a novel series of synthetic analogues of hGH-RH(1-29)NH₂. These analogues inhibit the activity of endogenous hGH-RH, and therefore prevent the release of growth hormone. This inhibition is believed to result from replacement of various amino acids and acylation with aromatic or nonpolar acids at the N-terminus of GH-RH(1-29)NH₂. The analogues exhibit prolonged antagonistic duration.

Specifically, the invention relates to peptides comprising the formulae:

α) X-R¹ -R² -R³ -R⁴ -R⁵ -R⁶ -Thr-R⁸ -R⁹ -R¹⁰ -R¹¹ -R¹² -Val-Leu-R¹⁵ -Gln-Leu-Ser-R¹⁹ -R²⁰ -R²¹ -Leu-Leu-Gln-Asp-Ile-R²⁷ -R²⁸ -R²⁹

wherein X is H, Ac, Aqc, IAc, BrProp, For, Ibu, Nac, 2-Nac, 1- or 2-Npt, 1- or 2-Npr, PhAc, Fpr, or any other aromatic or nonpolar acyl group,

R¹ is Tyr, His or Phe(Y), in which Y=H, F, Cl, Br, NO₂, NH₂, CH₃ or OCH₃,

R² is D-Arg, D-Cit, D-Har, D-Lys, D-Tic or D-Orn,

R³ is Asp, D-Asp, Ala, D-Ala or Gly,

R⁴ is Ala, Abu or Gly,

R⁵ is Ile, Ala or Gly,

R⁶ is Phe, Tic, Ala, Pro, Tpi, Nal or Phe(Y), in which Y=H, F, Cl, Br, NO₂, NH₂, CH₃ or OCH₃,

R⁸ is Asn, Gin, Ser, Thr, Val, Leu, lie, Ala, D-Ala, D-Asn, D-Gln, D-Thr, D-Leu, Abu, D-Abu, Nle, or Aib,

R⁹ is Ser

R¹⁰ is Tyr or Phe(Y), in which Y=H, F, Cl, Br, NO₂, CH₃ or OCH₃,

R¹¹ is Arg, D-Arg, or Cit,

R¹² is Lys, D-Lys, Cit, D-Cit, Orn, D-Orn, NIe or Ala,

R¹⁵ is Gly, Ala, Abu or GIn,

R¹⁹ is Ala or Abu,

R²⁰ is Arg, D-Arg or Cit,

R²¹ is Lys, D-Lys, Orn or Cit,

R²⁷ is Met, Nle or Abu,

R²⁸ is Ser, Asn, Asp, Ala or Abu,

R²⁹ is Agm, Arg-NH₂, Arg-OH, Cit-NH₂, Cit-OH, Har-NH₂ or Har-OH, and pharmaceutically acceptable salts thereof.

Among the preferred embodiment are peptides wherein X is PhAc or Ibu, R¹ is Tyr or His, R² is D-Arg or D-Cit, R³ is Asp, R⁴ is Ala, R⁵ is lie, R⁶ is Phe(pCI) or Nal, R⁸ is Asn, D-Asn, D-Thr or Abu, R¹⁰ is Tyr or Phe(pCI), R¹¹ is Arg, R¹² is Lys or D-Lys, R¹⁵ is Abu or Ala, R¹⁹ is Ala or Abu, R²⁰ is Arg, R²¹ is Lys, R²⁷ is Nle, R²¹ is Ser, Asp, or Abu, R²⁹ is Agm or Arg-NH₂.

Six very preferred embodiments have the formulae:

PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -1Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Asn⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Ala¹⁵ -Gln¹⁶ Leu¹⁷ Ser¹⁸ -Ala¹⁹ Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁵ -Ile²⁸ -Nle²⁷ -Asp²⁸ -Agm Peptide 5 PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Asn⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Abu¹⁵ -Gln¹⁶ -Leu¹⁷ -Serl¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁵ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Agm Peptide 8 Ibu⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Asn⁸ -Ser⁹ -Phe(pCl)¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Abu¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Lru²³ -Gln²⁴ -Asp²⁶ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Agm Peptide 6 PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Asn⁸ -Ser⁸ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Ala¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁵ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Arg²⁹ -NH₂ Peptide 9 PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Abu⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Ala¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁶ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Arg²⁹ -NH₂ Peptide 11 PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Abu⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Ala¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁵ -Ile²⁶ -Nle²⁷ -Abu²⁸ -Arg²⁹ -NH₂ Peptide 13

Under well-established convention, these may be abbreviated as follows:

PhAc⁰,D-Arg², Phe(pCl)⁶, Ala¹⁵, Nle²⁷, Asp²⁸ !hGH-RH(1-28)Agm Peptide 5

Ibu⁰,D-Arg², Phe(pCl)⁶,10, Abu¹⁵, Nle²⁷ !hGH-RH(1-28)Agm Peptide 6

PhAc⁰,D-Arg², Phe(pCl)⁶, Abu¹⁵, Nle²⁷ !hGH-RH(1-28)Agm Peptide 8

PhAc⁰,D-Arg², Phe(pCl)⁶, Ala¹⁵, Nle²⁷ !hGH-RH(1-29)-NH₂ Peptide 9

PhAc⁰,D-Arg², Phe(pCl)⁶,Abu⁸,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide 11

PhAc⁰,D-Arg², Phe(pCl)⁶, Abu⁸,28, Ala¹⁵, Nle²⁷ !hGH-RH(1-29)-NH₂ Peptide 13

β) X-A¹ -B² -A³ -R⁴ -R⁵ -R⁶ -Thr-A⁸ Ser-R¹⁰ -R¹¹ -B¹² -Val-Leu-R¹⁵ -A¹⁶ -A¹⁷ -Ser-R¹⁹ -B²⁰ -B²¹ -Leu-Leu-Gln-A²⁶ -Ile-R²⁷ -R²⁸ -B²⁹

wherein lactam bridge is formed between positions 1,2; 2,3; 8,12; 16,20; 17-21; 21,25; 25,29 or both 8,12 and 21,25 positions and

X is H, Ac, Aqc, IAc, BrProp, For, Ibu, Nac, 2-Nac, 1- or 2-Npt, 1- or 2-Npr, PhAc, Fpr or any other aromatic or nonpolar acyl group,

A is Glu, D-Glu, Gin, Asp, D-Asp, Asn, Abu, Leu, Tyr, His, Phe(Y), in which Y=H, F, Cl, Br, NO₂, NH₂, CH₃ or OCH₃, Ser, Thr, Val, lie, Ala, D-Ala, D-Asn, D-Gin, D-Thr, D-Leu, Abu, D-Abu, Nle, or Aib,

B is Lys, Lys-OH, Lys-NH₂, D-Lys, D-Lys-OH, D-Lys-NH₂, Arg, Arg-OH, Arg-NH₂, D-Arg, D-Arg-OH, D-Arg-NH₂, Orn, Orn-OH, Orn-NH₂, D-Orn, D-Orn-OH, D-Orn-NH₂, Har, Har-OH, Har-NH₂, or Agm

R⁴ is Ala, Abu or Gly,

R⁵ is Ile, Ala or Gly,

R⁶ is Phe, Tic, Tpi, Nal or Phe(Y), in which Y=H, F, Cl, Br, NO₂, NH₂, CH₃ or OCH₃,

R¹⁰ is Tyr or Phe(Y), in which Y=H, F, Cl, Br, NO₂, NH₂, CH₃ or OCH₃,

R¹⁵ is Gly, Ala, Abu or GIn,

R²⁷ is Met, Nle or Abu,

R²⁸ is Ser, Asn, Asp, Ala or Abu,

and pharmaceutically acceptable salts thereof.

Among the preferred embodiment are peptides wherein X is PhAc or Ibu, A¹ is Tyr, His, Glu, Asp or D-Asp, B² is D-Arg, D-Cit or D-Lys, A³ is Asp, R⁴ is Ala, R⁵ is Ile, R⁶ is Phe(pCl) or Nal, A⁸ is Asn, D-Asn, Abu, Asp, D-Asp, Glu or D-Glu, R¹⁰ is Tyr or Phe(4-Cl), R¹¹ is Arg, B¹² is Lys or D-Lys, R¹⁵ is Abu or Ala, A¹⁶ is Gln or Glu, A¹⁷ is Leu or Glu, R¹⁹ is Ala or Abu, B²⁰ is Arg or Lys, B²¹ is Lys, A²⁵ is Asp or Glu, R²⁷ is Nle, R²⁸ is Ser, Asp, or Abu, B²⁹ is Agm, Arg-NH₂ or Orn-NH₂ and lactam bridge is formed between positions 8,12; 17,21 or both 8,12 and 21,25 positions. Five very preferred embodiments have the formulae:

cyclo⁸,12 PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Glu⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Ala⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁵ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Arg-NH₂ Peptide 17

cyclo¹⁷,21 PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Ser⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Ala¹⁵ -Gln¹⁶ -Glu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁵ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Arg-NH₂ Peptide 18

cyclo⁸,12; 21,25 PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Glu⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Abu¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Glu²⁵ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Agm Peptide 21

cyclo⁸,12; 21,25 PhAc⁰ -Tyr¹ -D-Arg² -D-Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Glu⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -D-Lys¹² -Val¹³ -Leu¹⁴ -Ala¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Glu²⁵ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Arg²⁹ -NH₂ Peptide 22

cyclo⁸,12; 21,25 PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Glu⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -D-Lys¹² -Val¹³ -Leu¹⁴ -Ala¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Glu²⁵ -Ile²⁶ -Nle²⁷ -Ser²⁸ -Arg²⁹ -NH₂ Peptide 23

Under well-established convention, these may be abbreviated as follows:

cyclo⁸,12 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂ Peptide 17

cyclo¹⁷,21 PhAc⁰,D-Arg²,Phe(pCl)⁶,Ser⁸,Ala¹⁵,Glu¹⁷,Nle²⁷ !hGH-RH(1-29)-NH₂ Peptide 18

cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,25,Abu¹⁵,Nle²⁷ ! hGH-RH(1-28)Agm Peptide 21

cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,D-Asp³,Phe(pCl)⁶,Glu⁸,25,D-Lys.sup.12,Ala¹⁵, Nle²⁷ !hGH-RH(1-29)-NH₂ Peptide 22

cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,25,D-Lys¹²,Ala.sup.15,Nle²⁷ ! hGH-RH(1-29)-NH₂ Peptide 23

It is noted that the amino acid residues from 30 through 44 of the native GH-RH molecule do not appear to be essential to activity; nor does their identity appear to be critical. Therefore, it appears that the addition of some or all of these further amino acid residues to the C-terminus of the hGH-RH(1-29)-NH₂ analogues of the present invention will not affect the efficacy of these analogues as GH-RH antagonists. If some or all of these amino acids were added to the C-terminus of the hGH-RH(1-29)-NH₂ analogues, the added amino acid residues could be the same as residues 30 through 44 in the native hGH-RH sequence or reasonable equivalents.

Synthetic Methods.

The synthetic peptides are synthesized by a suitable method such as by exclusive solid phase techniques, by partial solid-phase techniques, by fragment condensation or by classical solution phase synthesis.

When the analogues of this invention are synthesized by solid-phase method, the C-terminus residue (here, R²⁹) is appropriately linked (anchored) to an inert solid support (resin) while bearing protecting groups for its alpha amino group (and, where appropriate, for its side chain functional group). After completion of this step, the alpha amino protecting group is removed from the anchored amino acid residue and the next amino acid residue, R²⁸, is added having its alpha amino group (as well as any appropriate side chain functional group) suitably protected, and so forth. The N-terminus protecting groups are removed after each residue is added, but the side chain protecting groups are not yet removed. After all the desired amino acids have been linked in the proper sequence, the peptide is cleaved from the support and freed from all side chain protecting group(s) under conditions that are minimally destructive towards residues in the sequence. This is be followed by a careful purification and scrupulous characterization of the synthetic product, so as to ensure that the desired structure is indeed the one obtained.

It is particularly preferred to protect the alpha amino function of the amino acids during the coupling step with an acid or base sensitive protecting group. Such protecting groups should have the properties of being stable in the conditions of peptide linkage formation, while being readily removable without destruction of the growing peptide chain and without racemization of any of the chiral centers contained therein. Suitable alpha amino protecting groups are Boc and Fmoc.

Medical Applications.

The hGH-RH antagonist peptides, or salts of these peptides, may be formulated in pharmaceutical dosage forms containing effective amounts thereof and administered to humans or animal for therapeutic or diagnostic purposes. The peptides may be used to suppress GH levels and to treat conditions associated with excessive levels of GH, e.g., diabetic retinopathy and nephropathy, and acromegaly. Also provided are methods for treating these diseases by administration of a composition of the invention to an individual needing such treatment. The main uses of GH-RH antagonists are however,in the field of cancer, for example human cancers of the breast, lung, colon, brain, and pancreas where the receptors for IGF-I are present.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of volume changes of SW 1990 human pancreatic cancers in nude mice during treatment with certain GH-RH antagonists against days of treatment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A. Abbreviations

The nomenclature used to define the peptides is that specified by the IUPAC-IUB Commissioner on Biochemical Nomenclature wherein, in accordance with conventional representation, the amino group at the N-terminus appears to the left and the carboxyl group at the C-terminus appears to the right. The term "natural amino acid" as used herein means one of the common, naturally occurring L-amino acids found in naturally occurring proteins: Gly, Ala, Val, Leu, Ile, Ser, Thr, Lys, Arg, Asp, Asn, Glu, Gln, Cys, Met Phe, Tyr, Pro, Trp and His. When the natural amino acid residue has isomeric forms, it is the L-form of the amino acid that is represented herein unless otherwise expressly indicated.

Non-coded amino acids, or amino acid analogues, are also incorporated into the GH-RH antagonists. ("Non-coded" amino acids are those amino acids which are not among the approximately 20 natural amino acids found in naturally occurring peptides.) Among the non-coded amino acids or amino acid analogues which may be used in the hGH-RH antagonist peptides are the following: by Abu is meant alpha amino butyric acid, by Agm is meant agmatine (1-amino-4-guanidino-butane), by Aib meant alpha amino isobutyric acid, by Har is meant homoarginine, by Nal is meant 2-naphthyl-alanine, by Nle is meant norleucine, and by Tic is meant 1,2,3,4-tetrahydroisoquinoline carboxilic acid. When these non-coded amino acids, or amino acid analogues, have isomeric forms, it is the L-form of the amino acid that is represented unless otherwise expressly indicated.

Abbreviations used herein are:

    ______________________________________                                         Abu         α-aminobutyric acid                                          Ac          acetyl                                                             AcOH        acetic acid                                                        Ac.sub.2 O  acetic anhydride                                                   Agm         agmatine (1-amino-4-guanidino-butane)                              Aib         α-aminoisobutyric acid                                       Aqc         anthraquinone-2-carbonyl                                           BHA         benzhydrylamine                                                    Boc         tert.butyloxycarbonyl                                              BOP         benzotriazole-1-yl-oxy-tris-(dimethylamino)-                                   phosphonium hexafluorophosphate                                    BrProp      bromopropionyl                                                     cHx         cyclohexyl                                                         Cit         citrulline (2-amino-5-ureidovaleric acid)                          DCM         dichloromethane                                                    DIC         N,N'-diisopropylcarbodiimide                                       DIEA        diisopropylethylamine                                              DMF         dimethylformamide                                                  Fpr         phenylpropionyl                                                    GH          growth hormone                                                     GH-RH       GH releasing hormone                                               Har         homoarginine                                                       HBTU        2-(1H-Benzotriazol-1-yl)-1,1,3,3-                                              tetramethyluronium hexaflourophosphate                             hGH-RH      human GH-RH                                                        HOBt        1-hydroxybenzotriazole                                             HPLC        high performance liquid chromatography                             IAc         iodoacetyl                                                         Ibu         isobutyryl                                                         MeOH        methanol                                                           MeCN        acetonitrile                                                       MBHA        para-methylbenzhydrylamine                                         Nac         1-naphthylacetyl                                                   2-Nac       2-naphthylacetyl                                                   Nal         2-naphthylalanine                                                  NMM         N-methylmorpholine                                                 Npr         naphthylpropionyl                                                  Npt         naphthoyl                                                          Phe(pCl)    para-chloro-phenylalanine                                          PhAc        phenylacetyl                                                       rGH-RH      rat GH-RH                                                          RP-HPLC     reversed phase HPLC                                                SPA         sulfophenoxy                                                       TFA         trifluoroacetic acid                                               Tic         1,2,3,4-tetrahydroisoquinoline                                     Tos         para-toluenesulfonyl                                               Tpi         2,3,4,9-tetrahydro-1H-pyrido 3,4-b!indol-3-                                    carboxylic acid                                                    Tyr(Me)     tyrosine methylether                                               Z           benzyloxycarbonyl                                                  ______________________________________                                    

B. The GH-RH Analogues

The hGH-RH analogues of the present invention were designed to increase the affinities of the peptides to the receptor, to improve metabolic stability and to maximize the amphiphilic secondary structure of the molecules. Many of these analogues cause very effective and long lasting inhibition of the GH release stimulated by hGH-RH(1-29)NH₂ in vitro and in vivo.

The following embodiments are specially preferred as having remarkable bioactivity:

Ibu⁰,D-Arg²,Phe(pCl)⁶,Abu¹⁵,Nle²⁷,Cit²⁹ !hGH-RH(1-29)-NH₂ Peptide # 1

Ibu⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,15,Nle²⁷,Cit²⁹ !hGH-RH(1-29)-NH₂ Peptide # 2

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,15,Nle²⁷,Cit²⁹ !hGH-RH(1-29)-NH₂ Peptide # 3

Ac-Nal⁰,D-Arg²,Phe(pCl)⁶,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 4

PhAc⁰,D-Arg²,Phe(pCl)⁶,Ala¹⁵,Nle²⁷,Asp²⁸ !hGH-RH(1-28)Agm Peptide # 5

Ibu⁰,D-Arg²,Phe(pCl)⁶,10,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 6

Ibu⁰,D-Arg²,Phe(pCl)⁶,D-Thr⁸,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 7

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 8

PhAc⁰,D-Arg²,Phe(pCl)⁶,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂ Peptide # 9

PhAc⁰,Tyr(Me),D-Arg²,Phe(pCl)⁶,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂ Peptide # 10

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,Ala¹⁵,Nle²⁷ !,hGH-RH(1-29)NH₂ Peptide # 11

PhAc⁰,D-Arg²,Nal⁶,Abu⁸,28,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 12

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,28,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 13

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,D-Lys¹²,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 14

PhAc⁰,D-Arg²,Phe(pCl)⁶,Orn¹²,21,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 15

Ibu⁰,D-Arg²,Phe(pCl)⁶,Orn¹²,21,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 16

cyclo⁸,12 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 17

cyclo¹⁷,21 PhAc⁰,D-Arg²,Phe(pCl)⁶,Ser⁸,Ala¹⁵,Glu¹⁷,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 18

cyclo²⁵,29 PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,Ala¹⁵,D-Asp²⁵,Nle²⁷,Orn²⁹ !hGH-RH(1-29)NH₂ Peptide # 19

cyclo²⁵,29 PhAc⁰,D-Arg²,Nal⁶,Abu⁸,Ala¹⁵,D-Asp²⁵,Nle.sup.27,Orn²⁹ !hGH-RH(1-29)NH₂ Peptide # 20

cyclo⁸,12;21,25 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,25,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 21

cyclo⁸,12;21,25 phAc⁰,D-Arg²,D-Asp³,Phe(pCl)⁶,Glu⁸,25,D-Lys.sup.12,Ala¹⁵,Glu²⁵,Nle²⁷,hGH-RH(1-29)NH₂ Peptide # 22

cyclo⁸,12;21,25,PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,25,D-Lys¹²,Ala²⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 23

cyclo⁸,12;21,25 PhAc⁰,D-Arg²,Phe(pCl)⁶,Asp⁸,D-Lys¹²,Ala¹⁵,Glu²⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 24

PhAc⁰,D-Arg²,Tic⁶,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 25

PhAc⁰,D-Tic²,Phe(pCl)⁶,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 26

C. Method of Preparation

1. Overview of Synthesis

The peptides are synthesized by a suitable method such as by exclusive solid phase techniques, by partial solid-phase techniques, by fragment condensation or by classical solution phase synthesis. For example, the techniques of exclusive solid-phase synthesis are set forth in the textbook "Solid Phase Peptide Synthesis", J. M. Stewart and J. D. Young, Pierce Chem. Company, Rockford, 111, 1984 (2nd. ed.), and M. Bodanszky, "Principles of Peptide Synthesis", SpringerVerlag, 1984. The hGH-RH antagonist peptides are preferably prepared using solid phase synthesis, such as that generally described by Merrifield, J.Am.Chem.Soc., 85, p. 2149 (1963), although other equivalent chemical syntheses known in the art can also be used as previously mentioned.

The synthesis is carried out with amino acids that are protected at their alpha amino group. Urethane type protecting groups (Boc or Fmoc) are preferably used for the protection of the alpha amino group. The preferred protecting group is Boc.

In solid phase synthesis, the N-alpha-protected amino acid moiety which forms the aminoacyl group of the final peptide at the C-terminus is attached to a polymeric resin support via a chemical link. After completion of the coupling reaction, the alpha amino protecting group is selectively removed to allow subsequent coupling reactions to take place at the amino-terminus, preferably with 50% TFA in DCM when the N-alpha-protecting group is Boc. The remaining amino acids with similarly Boc-protected alpha amino groups are coupled stepwise to the free amino group of the preceding amino acid on the resin to obtain the desired peptide sequence. Because the amino acid residues are coupled to the alpha amino group of the C-terminus residue, growth of the synthetic hGH-RH analogue peptides begins at the C terminus and progresses toward the N-terminus. When the desired sequence has been obtained, the peptide is acylated, if appropriate, and it is removed from the support polymer.

Each protected amino acid is used in excess (2.5 or 3 equivalents) and the coupling reactions are usually carried out in DCM, DMF or mixtures thereof. The extent of completion of the coupling reaction is monitored at each stage by the ninhydrin reaction. In cases where incomplete coupling is determined, the coupling procedure is repeated before removal of the alpha amino protecting group prior to the coupling of the next amino acid.

A typical synthesis cycle is shown in Table I.

                  TABLE I                                                          ______________________________________                                         Protocol for a Typical Synthetic Cycle Using Boc-strategy                      Step       Reagent          Mixing Time (min)                                  ______________________________________                                         1. Deprotection                                                                           50% TFA in DCM    5 + 25                                                       DCM wash         1                                                             2-propanol wash  1                                                  2. Neutralization                                                                         5% DIEA in DCM   1                                                             DCM wash         1                                                             MeOH wash        1                                                             5% DIEA in DCM   3                                                             MeOH wash        1                                                             DCM wash (3 times)                                                                              1-1                                                3. Coupling                                                                               3 equiv. Boc-amino acid in                                                     DCM or DMF + 3 equiv. DIC                                                      or the preformed                                                               HOBt ester of the Boc-amino                                                                     60                                                            acid                                                                           MeOH wash        2                                                             DCM wash         2                                                  4. Acetylation                                                                            Ac.sub.2 O in DCM (30%)                                                                         10 + 20                                            (if appropriate)                                                                          MeOH wash (3 times)                                                                             2                                                             DCM wash (3 times)                                                                              2                                                  ______________________________________                                    

After completion of the synthesis, the cleavage of the peptide from the resin can be effected using procedures well known in peptide chemistry.

Some of the amino acid residues of the peptides have side chain functional groups which are reactive with reagents used in coupling or deprotection. When such side chain groups are present, suitable protecting groups are joined to these functional groups to prevent from undesirable chemical reactions occurring during the reactions used to form the peptides. The following general rules are followed in selecting a particular side chain protecting group: (a) the protecting group preferably retains its protecting properties and is not split off under coupling conditions, (b) the protecting group should be stable in conditions for removing the alpha amino protecting group at each step of the synthesis, (c) the side chain protecting group must be removable upon the completion of the synthesis of the desired amino acid sequence, under reaction conditions that will not undesirably alter the peptide chain.

The initial synthetic steps utilized herein are disclosed in U.S. Pat. No. 4,914,189 which is incorporated by reference herein. Reference is particularly made to Examples I through IV therein.

The reactive side chain functional groups are preferably protected as follows: benzyl for Thr and Ser; 2,6-dichlorobenzyloxycarbonyl for Tyr; p-toluene-sulfonyl for Arg; 2-chlorobenzyloxycarbonyl or fluorenylmethyloxy carbonyl for Lys, Orn; and cyclohexyl or fluorenylmethyl for Asp and Glu. The side chains of Asn and Gln are unprotected.

2. Coupling R²⁹ to the support Polymer

The hGH-RH antagonist peptides may be synthesized on a variety of support polymers. These support polymers may be amino resins such as amino-methyl resins, benzhydrylamine resins, p-methylbenzhydrylamine resins and the like. Boc-R²⁹ is the initial material joined to the support phase, suitably Boc-Arg(Tos)-OH or Boc-Agm.

For the synthesis of peptides having Agm at the C-terminus, it is preferred that the support phase SP! is an amino methyl resin. The guanidino group of Boc-Agm is joined to the support polymer via a stable but readily cleavable bridging group. It has been found that such a bridge may be readily provided by the sulfonyl phenoxy acetyl moiety. The alpha amino Boc-protected Agm is reacted with the chlorosulfonyl phenoxy acetic acid

    Cl--SO.sub.2 --φ--O--CH.sub.2 --COOH

to form

    Boc--Agm.sup.29 --SO.sub.2 --φ--O--CH.sub.2 --COOH.

This compound is then coupled to the support polymer SP! using DIC or BOP as activating reagent to yield:

    Boc-Agm.sup.29 --SO.sub.2 --φ--O--CH.sub.2 --CO-- SP!

For the synthesis of peptides having Arg-NH₂ at the C-terminus, Boc-Arg(Tos)--OH is coupled to the neutralized BHA or MBHA resin using DIC or BOP as activating reagent.

3. Stepwise Coupling of Amino Acid Residues.

Utilizing the Boc-protected Agm resin (California Peptide Res. Inc.), (or the Boc-Arg(Tos)-resin), the peptide itself may suitably be built up by solid phase synthesis in the conventional manner. The selection of an appropriate coupling reagent is within the skill of the art. Particularly suitable as coupling reagents are N,N'-diisopropyl carbodiimide (DIC) or the BOP carboxyl activating reagent.

Each protected amino acid is coupled in about a three-fold molar excess, with respect to resin-bound aminoacyl residue(s), and the coupling may be carried out in a medium such as DMF: CH₂ Cl₂ (1:1) or in DMF or CH₂ Cl₂ alone. In cases where incomplete coupling occurs, the coupling procedure is repeated before removal of the alpha amino protecting group. The success of the coupling reaction at each stage of the synthesis is preferably monitored by the ninhydrin reaction.

In case of lactam bridge formation, the side-chain protecting groups (Fmoc and OFm) of Lys or Orn and Asp or Glu respectively of the Boc-protected peptide-resin are selectively removed with 20% piperidine in DMF. Formation of lactam bridge is achieved on the solid support using HBTU coupling agent.

4. Removal of the Peptide from the Support Polymer.

When the synthesis is complete, the peptide is cleaved from the support phase. Removal of the peptide from the resin is performed by treatment with a reagent such as liquid hydrogen fluoride which also cleaves all remaining side chain protecting groups.

Suitably, the dried and protected peptide-resin is treated with a mixture consisting of 1.0 mL m-cresol and 10 mL anhydrous hydrogen fluoride per gram of peptide-resin for 60 min at 0° C. to cleave the peptide from the resin as well as to remove all side chain protecting groups. After the removal of the hydrogen fluoride under a stream of nitrogen and vacuum, the free peptides are precipitated with ether, filtered, washed with ether and ethyl acetate, extracted with 50% acetic acid, and lyophilized.

5. Purification

The purification of the crude peptides can be effected using procedures well known in peptide chemistry. For example, purification may be performed on a MacRabbit HPLC system (Rainin Instrument Co. Inc., Woburn, Mass.) with a Knauer UV Photometer and a Kipp and Zonen BD40 Recorder using a 10×250 mm VYDAC 228TP column packed with C8 silica gel (300 Å pore size, 10 μm particle size) (Rainin Inc.) The column is eluted with a solvent system consisting of (A) 0.1% aqueous TFA and (B) 0.1% TFA in 70% aqueous MeCN in a linear gradient mode (e.g., 30-65% B in 120 min). The eluent is monitored at 220 nm, and fractions are examined by analytical HPLC using a Hewlett-Packard Model HP-1090 liquid chromatograph and pooled to give maximum purity. Analytical HPLC is carried out on a W-Porex C18 reversed-phase column (4.6×250 mm, 5 μm particle size, 300 Å pore size) (Phenomenex, Rancho Palos Verdes, Calif.) using isocratic elution with a solvent system consisting of (A) and (B) defined above. The peaks are monitored at 220 and 280 nm. The peptides are judged to be substantially (>95%) pure by analytical HPLC. The expected amino acid composition is also confirmed by amino acid analysis.

D. Pharmaceutical Composition

The peptides of the invention may be administered in the form of pharmaceutically acceptable, nontoxic salts, such as acid addition salts. Illustrative of such acid addition salts are hydrochloride, hydrobromide, sulphate, phosphate, fumarate, gluconate, tannate, maleate, acetate, citrate, benzoate, succinate, alginate, pamoate, malate, ascorbate, tartarate, and the like. Particularly preferred antagonists are salts of low solubility, e.g., pamoate salts and the like. These exhibit long duration of activity.

The compounds of the present invention are suitably administered to subject humans or animals s.c., i.m., or i.v; intranasally or by pulmonary inhalation; or in a depot form (e.g., microcapsules, microgranules, or cylindrical rod like implants) formulated from a biodegradable suitable polymer (such as D,L-lactide-coglycolide), the former two depot modes being preferred. Other equivalent modes of administration are also within the scope of this invention, i.e., continuous drip, depot injections, infusion pump and time release modes such as microcapsules and the like. Administration is in any physiologically acceptable injectable carrier, physiological saline being acceptable, though other carriers known to the art may also be used.

The peptides are preferably administered parenterally, intramuscularly, subcutaneously or intravenously with a pharmaceutically acceptable carrier such as isotonic saline. Alternatively, the peptides may be administered as an intranasal spray with an appropriate carrier or by pulmonary inhalation. One suitable route of administration is a depot form formulated from a biodegradable suitable polymer, e.g., poly-D,L-lactide-coglycolide as microcapsules, microgranules or cylindrical implants containing dispersed antagonistic compounds.

The amount of peptide needed depends on the mode of administration and the intended result. In general, the dosage range is between 1-100 μg/kg of body weight of the host per day.

E. Therapeutic Uses of GH-RH Antagonists

hGH-RH antagonists can be used in treatment of conditions caused by excess growth hormone, for example acromegaly, which is manifested by an abnormal enlargement of the bones of the face and extremities. The GH-RH antagonists may also be used to treat diabetic nephropathy (the main cause of blindness in diabetics) and diabetic retinopathy, in which damage to the eye and kidney respectively is thought to be due to GH.

The hGH-RH antagonists are designed to block the binding and therefore the action of GH-RH, which stimulates the secretion of GH, which in turn stimulates production of IGF I. GH-RH antagonists may be administered alone or together with somatostatin analogues, a combination which more completely suppresses IGF-I levels. It is advantageous to administer antagonists of GH-RH rather than somatostatin due to the fact that GH-RH antagonists may be utilized in situations where target sites do not have somatostatin receptors.

However, the main applications of GH-RH antagonists are in the field of cancer. This is based on the following considerations: GH-RH antagonists are designed to block the binding and therefore the action of GH-RH, which stimulates the secretion of GH, which in turn stimulates production of insulin-like growth factor I (IGF-I) also called somatomedin-C. The involvement of IGF-I (somatomedin-C) in breast cancer, prostate cancer, colon cancer, bone tumors and other malignancies is well established, and somatostatin analogues alone do not adequately suppress GH and IGF-I levels. A complete suppression of IGF-I levels or secretion is required for a better inhibition of tumor growth. Autocrine production of IGF-I by various tumors could be also under control of GH-RH and might therefore be inhibited by GH-RH antagonists. GH-RH antagonists might also inhibit the production of IGF-I. A more detailed theoretical background of the applications of GH-RH in the field of oncology (cancer) is as follows: The receptors for IGF-I are present in primary human breast cancers, in lung cancers, in human colon cancers, in human brain tumors, and in human pancreatic cancers.

The presence of IGF-I receptors in these tumors appears to be related to malignant transformation and proliferations of these cancers. IGF-I can act as endocrine, paracrine or autocrine growth factor for various human cancers, that is the growth of these neoplasms is dependent on IGF-I. GH-RH antagonists by suppressing GH secretion would lower the production of IGF-I. Since IGF-I stimulates growth of these various neoplasms (cancers), the lowering of circulating IGF-I levels should lead to tumor growth inhibition. It is possible that GH-RH antagonists could also lower paracrine or autocrine production of IGF-I by the tumors, which should also lead to inhibition of cancer proliferation. These views are in accordance with modern concepts of clinical oncology. GH-RH antagonists should be given alone or together with somatostatin analogues and a combination would achieve a more complete suppression of IGF-I levels, elimination of tissue IGF-I levels, e.g., in human osteosarcomas, as well as breast cancer, colon cancer, prostate cancer, and non-small cell lung cancer (non-SCLC).

The advantage of GH-RH antagonists over somatostatin analogues is based on the fact that GH-RH antagonists may be utilized for suppression of tumors which do not have somatostatin receptors, for example human osteogenic sarcomas.

The present invention is described in connection with the following examples which are set forth for the purposes of illustration only. In the examples, optically active protected amino acids in the L-configuration are used except where specifically noted.

The following Examples set forth suitable methods of synthesizing the novel GH-RH antagonists by the solid-phase technique.

EXAMPLE I

Synthesis of Boc-agmatine

EXAMPLE II

Synthesis of 4-Chlorosulfonyl Phenoxyacetic Acid (CI-SPA)

EXAMPLE III

Boc-agmatine- SPA!

EXAMPLE IV

Coupling of Boc-agmatine- SPA! to Support Phase

The initial synthetic sequence utilized herein and indicated by headings above is disclosed in Examples I through IV of U.S. Pat. No. 4,914,189, which Examples are incorporated herein by reference.

EXAMPLE V

Ibu-Tyr¹ -D-Arg² -Asp³ -Ala⁴ -Ile⁵ -Phe(pCl)⁶ -Thr⁷ -Asn⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Abu¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁵ -lle²⁶ -Nle²⁷ -Ser²⁸ -Cit²⁹ -NH₂ (Peptide 1)

( Ibu⁰,D-Arg²,Phe(pCl)⁶,Abu¹⁵,Nle²⁷,Cit²⁹ !hGH-RH(1-29)NH₂)

The synthesisis is conducted in a stepwise manner using manual solid phase peptide synthesis equipment. Briefly, benzhydrylamine (BHA) resin (Bachem, Calif.) (100 mg, 0.044 mmole) is neutralized with 5% DIEA in CH₂ Cl₂ and washed according to the protocol described in Table 1. The solution of Boc-Cit-OH (61mg, 0.25 mmole) in DMF-CH₂ Cl₂ (1:1) is shaken with the neutralized resin and DIC (44 μL, 0.275 mmole) in a manual solid phase peptide synthesis equipment for 1 hour. After the completion of the coupling reaction is proved by negative ninhydrin test, deprotection with 50% TFA in CH₂ Cl₂, and neutralization with 5% DIEA in CH₂ Cl₂, the peptide chain is built stepwise by coupling the following protected amino acids in the indicated order on the resin to obtain the desired peptide sequence: Boc-Ser (Bzl)-OH, Boc-Nle-OH, Boc-lle-OH, Boc-Asp(OcHx)-OH, Boc-Gln-OH, Boc-Leu-OH, Boc-Leu-OH, Boc-Lys(2-Cl-Z)-OH, Boc-Arg(Tos)-OH, Boc-Ala-OH, Boc-Ser(Bzl)-OH, Boc-Leu-OH, Boc-Gln-OH, Boc-Abu-OH, Boc-Leu-OH, Boc-Val-OH, Boc-Lys(2-Cl-Z)-OH, Boc-Arg(Tos)-OH, Boc-Tyr(2,6-diCl-Z)-OH, Boc-Ser(Bzl)-OH, Boc-Asn-OH, Boc-Thr(Bzl)-OH, Boc-Phe(pCl)-OH, Boc-lle-OH, Boc-Ala-OH, Boc-Asp(OcHx)-OH, Boc-D-Arg(Tos)-OH, Boc-Tyr(2,6-diCl-Z)-OH.

These protected amino acid residues (also commonly available from Bachem Co.) are represented above according to a well accepted convention. The suitable protecting group for the side chain functional group of particular amino acids appears in parentheses. The OH groups in the above formulae indicate that each residue's carboxyl terminus is free.

The protected amino acids (0.25 mmole each) are coupled with DIC (44 μL, 0.275 mmole) with the exceptions of Boc-Asn-OH and Boc-Gln-OH which are coupled with their preformed HOBt esters. After removal of the N.sup.α -Boc protecting group from Tyr¹, the peptide is acylated with isobutyric acid (Ibu) (75 mg, 0.4 mmole) using DIC (70 μL, 0.44 mmole).

In order to cleave the peptide from the resin and deprotect it, the dried peptide resin (138 mg) is stirred with 0.5 mL m-cresol and 5 mL hydrogen fluoride (HF) at 0° C. for 1 hour. After evaporation of the HF under vacuum, the remnant is washed with dry diethyl ether and ethyl acetate. The cleaved and deprotected peptide is dissolved in 50% acetic acid and separated from the resin by filtration. After dilution with water and lyophilization, 34 mg crude product is obtained.

The crude peptide is checked by analytical HPLC using a Hewlett-Packard Model HP-1090 liquid chromatograph with a W-Porex C18 reversed-phase column (4.6×250 mm, 5 μm particle size, 300 Å pore size from Phenomenex, Rancho Palos Verdes, Calif.) and linear gradient elution, (e.g., 40-70% B) with a solvent system consisting of (A) 0.1% aqueous TFA and (B) 0.1% TFA in 70% aqueous MeCN. 34 mg of the crude peptide is dissolved in AcOH/H₂ O, stirred, filtered and applied on a VYDAC 228TP column (10×250 mm) packed with C8 silica gel. The column is eluted with a solvent system described above in a linear gradient mode (e.g., 30-55% B in 120 min); flow rate 2 mL/min. The eluent is monitored at 220 nm, and fractions are examined by analytical HPLC. Fractions with purity higher than 95% are pooled and lyophilized to give 1.2 mg pure product. The analytical HPLC is carried out on a W-Porex C18 reversed-phase column described above using isocratic elution with a solvent system described above with a flow rate of 1.2 mL/min. The peaks are monitored at 220 and 280 nm. The product is judged to be substantially (>95%) pure by analytical HPLC. The expected amino acid composition is also confirmed by amino acid analysis.

Peptides 2 and 3 are synthesized in the same manner as Peptide 1, except that Boc-Asn-OH⁸ is replaced with Boc-Abu-OH (0.25 mmole) and the resulting peptides are acylated with isobutyric acid or phenylacetic acid repectively, to yield:

Ibu⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,15,Nle²⁷,Cit²⁹ !hGH-RH(1-29)-NH₂ Peptide # 2

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,15,Nle²⁷,Cit²⁹ !hGH-RH(1-29)-NH₂ Peptide # 3

EXAMPLE VI

PhAc⁰ -Tyr¹ -D-Arg² -Asp³ -Ala⁴ -lle⁵ -Phe(pCl)⁶ -Thr⁷ -Asn⁸ -Ser⁹ -Tyr⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Abu¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ Asp²⁵ -lle²⁶ -Nle²⁷ -Ser²⁸ -Agm²⁹ (Peptide 8)

or PhAc⁰,D-Arg², Phe(pCl)⁶,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm

The synthesisis is conducted in a stepwise manner using manual solid phase peptide synthesis equipment. Briefly, Boc-Agm-SPA-aminomethyl resin (California Peptide Research Co., Inc., California) (200 mg, 0.06 mmole) is deprotected with 50% TFA in CH₂ Cl₂, neutralized with 5% DIEA in CH₂ Cl₂, and washed as described in Table 1. The solution of Boc-Ser(Bzl)-OH (55 mg, 0.18 mmole) in DMF-CH₂ Cl₂ (1:1) is shaken with the H-Agm-SPA-aminomethyl resin and DIC (31 μL, 0.2 mmole) in a manual solid phase peptide synthesis equipment for 1 hour. After the completion of the coupling reaction is proved by negative ninhydrin test, deprotection with 50% TFA in CH₂ Cl₂ and neutralization with 5% DIEA in CH₂ Cl², and washed as described in Table I to build the peptide chain step-wise by coupling the following protected amino acids in the indicated order on the resin: Boc-Nle-OH, Boc-lle-OH, Boc-Asp(OcHx)-OH, Boc-Gln-OH, Boc-Leu-OH, Boc-Leu-OH, Boc-Lys(2-Cl-Z)-OH, Boc-Arg(Tos)-OH, Boc-Ala-OH, Boc-Ser(Bzl)-OH, Boc-Leu-OH, Boc-Gln-OH, Boc-Abu-OH, Boc-Leu-OH, Boc-Val-OH, Boc-Lys(2-Cl-Z)-OH, Boc-Arg(Tos)-OH, Boc-Tyr(2,6-diCl-Z)-OH, Boc-Ser(Bzl)-OH, Boc-Asn-OH, Boc-Thr(Bzl)-OH, Boc-Phe(pCl)-OH, Boc-lle-OH, Boc-Ala-OH, Boc-Asp (OcHx)-OH, Boc-D-Arg(Tos)-OH and Boc-Tyr(2,6-diCl-Z)-OH.

The protected amino acids (0.18 mmole each) are coupled with DIC (31 μL, 0.2 mmole) with the exceptions of Boc-Asn-OH and Boc-Gln-OH which are coupled with their preformed HOBt esters. After removal of the N.sup.α -Boc protecting group from Tyr¹, the peptide is acylated with phenylacetic acid (66 mg, 0.5 mmole) using DIC (88 μL, 0.55 mmole) as coupling agent.

In order to cleave the peptide from the resin and deprotect it, the dried peptide resin (148 mg) is stirred with 0.5 mL m-cresol and 5 mL hydrogen fluoride (HF) at 0° C. for 1 hour. After evaporation of the HF under vacuum, the remnant is washed with dry diethyl ether and ethyl acetate. The cleaved and deprotected peptide is dissolved in 50% acetic acid and separated from the resin by filtration. After dilution with water and lyophilization, 62 mg crude product is obtained.

62 mg of the GH-RH antagonist peptide is dissolved in AcOH/H₂ O and purified by RP-HPLC using the same procedure and equipments described in Example V. The product is judged to be substantially (>95%) pure by analytical HPLC. Confirmation of the structure is provided by amino acid analysis.

Peptides 4, 5, 6, 7, 15, 16, 25 and 26 are synthesized in the same manner as Peptide 1, except that these peptides also contain other substitutions, to yield:

Ac-Nal⁰,D-Arg²,Phe(pCl)⁶,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 4

PhAc⁰,D-Arg²,Phe(pCl)⁶,Ala¹⁵,Nle²⁷,Asp²⁸ !hGH-RH(1-28)Agm Peptide 5

Ibu⁰,D-Arg²,Phe(pCl)⁶,10,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide # 6

Ibu⁰,D-Arg²,Phe(pCl)⁶,D-Thr⁸,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide 7

PhAc⁰,D-Arg²,Phe(pCl)⁶,Orn¹²,21,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide 15

Ibu⁰,D-Arg²,Phe(pCl)⁶,Orn¹²,21,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm Peptide 16

PhAc⁰,D-Arg²,Tic⁶,Abu¹⁵,Nle²⁷) hGH-RH (1-28)Agm Peptide 25

PhAc⁰,D-Tic²,Phe(pCl)⁶,Abu¹⁵,Nle²⁷)!hGH-RH (1-28)Agm Peptide 26

EXAMPLE VII

PhAc-Tyr¹ -D-Arg² -Asp³ -Ala⁴ -lle⁵ -Phe(pCl)⁶ -Thr⁷ -Asn⁸ -Ser⁹ -Tyr¹⁰ -Arg¹¹ -Lys¹² -Val¹³ -Leu¹⁴ -Ala¹⁵ -Gln¹⁶ -Leu¹⁷ -Ser¹⁸ -Ala¹⁹ -Arg²⁰ -Lys²¹ -Leu²² -Leu²³ -Gln²⁴ -Asp²⁵ -lle²⁶ -Nle²⁷ -Ser²⁸ -Arg²⁹ -NH₂ (Peptide 9)

or PhAco⁰,D-Arg²,Phe(pCel)⁶,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂

The synthesis is conducted in a stepwise manner using manual solid phase peptide synthesis equipment. Briefly, benzhydrylamine (BHA) resin (Bachem, Calif.) (100 mg, 0.044 mmole) is neutralized with 5% DIEA in CH₂ Cl₂ and washed according to the protocol described in Table 1. The solution of Boc-Arg(Tos)-OH (107 mg, 0.25 mmole) in DMF-CH₂ Cl₂ (1:1) is shaken with the neutralized resin and DIC (44 μL, 0.275 mmole) in a manual solid phase peptide synthesis equipment for 1 hour. After the completion of the coupling reaction is proved by negative ninhydrin test, deprotection with 50% TFA in CH₂ Cl₂, and neutralization with 5% DIEA in CH₂ Cl₂, the peptide chain is built stepwise by adding the following protected amino acids in the indicated order on the resin to obtain the desired peptide sequence: Boc-Ser(Bzl)-OH, Boc-Nle-OH, Boc-lle-OH, Boc-Asp(OcHx)-OH, Boc-Gln-OH, Boc-Leu-OH, Boc-Leu-OH, Boc-Lys(2-CI-Z)-OH, Boc-Arg(Tos)-OH, Boc-Ala-OH, Boc-Ser(Bzl)-OH, Boc-Leu-OH, Boc-Gln-OH, Boc-Ala-OH, Boc-Leu-OH, Boc-Val-OH, Boc-Lys(2-Cl-Z)-OH, Boc-Arg(Tos)-OH, Boc-Tyr(2,6-diCl-Z)-OH, Boc-Ser(Bzl)-OH, Boc-Asn-OH, Boc-Thr(Bzl)-OH, Boc-Phe(pCl)-OH, Boc-lle-OH, Boc-Ala-OH, Boc-Asp(OcHx)-OH, Boc-D-Arg(Tos)-OH, Boc-Tyr(2,6-diCl-Z)-OH.

The protected amino acids (0.25 mmole each) are coupled with DIC (44 μL, 0.275 mmole) with the exceptions of Boc-Asn-OH and Boc-Gln-OH which are coupled with their preformed HOBt esters. After removal of the N.sup.α -Boc protecting group from Tyr¹, the peptide is acylated with phenylacetic acid (PhAc) (54 mg, 0.4 mmole) using DIC (70 μL, 0.44 mmole).

In order to cleave the peptide from the resin and deprotect it, the dried peptide resin (171 mg) is stirred with 0.5 mL m-cresol and 5 mL hydrogen fluoride (HF) at 0° C. for 1 hour. After evaporation of the HF under vacuum, the remnant is washed with dry diethyl ether and ethyl acetate. The cleaved and deprotected peptide is dissolved in 50% acetic acid and separated from the resin by filtration. After dilution with water and lyophilization, 98 mg crude product is obtained.

The crude peptide is checked by analytical HPLC using a Hewlett-Packard Model HP-1090 liquid chromatograph with a W-Porex C18 reversed-phase column (4.6×250 mm, 5 μm particle size, 300 Å pore size from Phenomenex, Rancho Palos Verdes, Calif.) and linear gradient elution, (e.g., 40-70% B) with a solvent system consisting of (A) 0.1% aqueous TFA and (B) 0.1% TFA in 70% aqueous MeCN. 60 mg of the crude peptide is dissolved in AcOH/H₂ O, stirred, filtered and applied on a VYDAC 228TP column (10×250 mm) packed with C8 silica gel. The column is eluted with a solvent system described above in a linear gradient mode (e.g., 30-55% B in 120 min); flow rate 2 mL/min. The eluent is monitored at 220 nm, and fractions are examined by analytical HPLC. Fractions with purity higher than 95% are pooled and lyophilized to give 2.6 mg pure product. The analytical HPLC is carried out on a W-Porex C18 reversed-phase column described above using isocratic elution with a solvent system described above with a flow rate of 1.2 mL/min. The peaks are monitored at 220 and 280 nm. The peptide is judged to be substantially (>95%) pure by analytical HPLC. The expected amino acid composition is also confirmed by amino acid analysis.

Peptides 10, 11, 12, 13, and 14 are synthesized in the same manner as Peptide 9, except that these peptides also contain other substitutions, to yield:

PhAc⁰,Tyr(Me),D-Arg²,Phe(pCl)⁶ Ala¹⁵, Nle²⁷ !hGH-RH(1-29)-NH₂ Peptide 10

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,Ala¹⁵,Nle²⁷ !,hGH-RH(1-29)NH₂ Peptide 11

PhAc⁰,D-Arg²,Nal⁶,Abu⁸,28,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide 12

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,28,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide 13

PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,D-Lys¹²,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂ Peptide 14

EXAMPLE VIII ##STR1##

The synthesis is conducted in a stepwise manner using manual solid phase peptide synthesis equipment. Briefly, benzhydrylamine (BHA) resin (Bachem, Calif.) (100 mg, 0.044 mmole) is neutralized with 5% DIEA in CH₂ Cl₂ and washed according to the protocol described in Table 1. The solution of Boc-Arg(Tos)-OH (107 mg, 0.25 mmole) in DMF-CH₂ Cl₂ (1:1) is shaken with the neutralized resin and DIC (44 μL, 0.275 mmole) in a manual solid phase peptide synthesis equipment for 1 hour. After the completion of the coupling reaction is proved by negative ninhydrin test, deprotection with 50% TFA in CH₂ Cl₂, and neutralization with 5% DIEA in CH₂ Cl₂, the peptide chain is built stepwise by coupling the following protected amino acids in the indicated order on the resin to obtain the desired peptide sequence: Boc-Ser(Bzl)-OH, Boc-Nle-OH, Boc-lle-OH, Boc-Asp(OcHx)-OH, Boc-Gln-OH, Boc-Leu-OH, Boc-Leu-OH, Boc-Lys(Fmoc)-OH, Boc-Arg(Tos)-OH, Boc-Ala-OH, Boc-Ser(Bzl)-OH, Boc-Glu(Fm)-OH, Boc-Gln-OH, Boc-Ala-OH, Boc-Leu-OH, Boc-Val-OH, Boc-Lys(2-Cl-Z)-OH, Boc-Arg(Tos)-OH, Boc-Tyr(2,6-diCl-Z)-OH, Boc-Ser(Bzl)-OH, Boc-Ser(Bzl)-OH, Boc-Thr(Bzl)-OH, Boc-Phe(pCl)-OH, Boc-lle-OH, Boc-Ala-OH, Boc-Asp(OcHx)-OH, Boc-D-Arg(Tos)-OH, Boc-Tyr(2,6-diCl-Z)-OH.

The protected amino acids (0.25 mmole each) are coupled with DIC (44 μuL, 0.275 mmole) with the exceptions of Boc-Asn-OH and Boc-Gln-OH which are coupled with their preformed HOBt esters. After removal of the N.sup.α -Boc protecting group from Tyr¹, the peptide is acylated with phenylacetic acid (PhAc) (75 mg, 0.4 mmole) using DIC (70 μL, 0.44 mmole). The acylated peptide is deprotected with 20% piperidine in DMF for 1 plus 20 minutes to give free side-chains of Glu¹⁷ and Lys²¹. After washing the resin, lactam bridge is formed with HBTU reagent (110 mg, 0.275 mmole) in DMF-DCM (1:1) containing DIEA (137 μL, 0.55 mmole) and HOBt (39 mg, 0.275 mmole) for 3 hours (negative Kaiser ninhydrin test).

In order to cleave the peptide from the resin and deprotect it, the dried peptide resin (53.1 mg) is stirred with 0.5 mL m-cresol and 5 mL hydrogen fluoride (HF) at 0° C. for 1 hour. After evaporation of the HF under vacuum, the remnant is washed with dry diethyl ether and ethyl acetate. The cleaved and deprotected peptide is dissolved in 50% acetic acid and separated from the resin by filtration. After dilution with water and lyophilization, 13.7 mg crude product is obtained.

The crude peptide is checked by analytical HPLC using a Hewlett-Packard Model HP-1090 liquid chromatograph with a W-Porex C18 reversed-phase column (4.6×250 mm, 5 μm particle size, 300 Å pore size from Phenomenex, Rancho Palos Verdes, Calif.) and linear gradient elution, (e.g., 40-70% B) with a solvent system consisting of (A) 0.1% aqueous TFA and (B) 0.1% TFA in 70% aqueous MeCN. The crude peptide is dissolved in AcOH/H₂ O, stirred, filtered and applied on a VYDAC 228TP column (10×250 mm) packed with C8 silica gel. The column is eluted with a solvent system described above in a linear gradient mode (e.g., 30-55% B in 120 min); flow rate 2 mL/min. The eluent is monitored at 220 nm, and fractions are examined by analytical HPLC. Fractions with purity higher than 95% are pooled and lyophilized to give 0.96 mg pure product. The analytical HPLC is carried out on a W-Porex C18 reversed-phase column described above using isocratic elution with a solvent system described above with a flow rate of 1.2 mL/min. The peaks are monitored at 220 and 280 nm. The peptide is judged to be substantially (>95%) pure by analytical HPLC. The expected amino acid composition is also confirmed by amino acid analysis.

Peptides 17,19 and 20 are synthesized in the same manner as Peptide 18, except that in addition to other substitutions lactam bridge is formed between positions 8,12 or 25,29, to yield:

cyclo⁸,12 PhAc⁰, D-Arg², Phe(pCl)⁶, Glu⁸, Ala¹⁵, Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 17

cycl²⁵,28 PhAc⁰, D-Arg², Phe(pCl)⁶, Abu⁸ Ala¹⁵, D-Asp²⁵, Nle²⁷, Orn²⁹ !hGH-RH(1-29)NH₂ Peptide # 19

cyclo²⁵,29 PhAc⁰, D-Arg²,Nal⁶, Abu⁸, Ala¹⁵, D-Asp²⁵, Nle²⁷, Orn²⁹ !hGH-RH(1-29)NH₂ Peptide # 20

Peptides 21,22,23, and 24 are synthesized in the same manner as Peptide 18, except that in addition to other substitutions lactam bridge is formed between both 8,12 and 21,25 positions, to yield:

cyclo⁸,12; 21,25 PhAc⁰, D-Arg², Phe(pCl)⁶, Glu⁸,25, Abu¹⁵, Nle²⁷ !hGH-RH(1-28)Agm Peptide #21

cyclo⁸,12; 21,25 PhAc⁰, D-Arg², D-Asp³, Phe(pCl)⁶, Glu⁸,25, D-Lys¹², Ala¹⁵, Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 22

cyclo⁸,22; 21,25 PhAc⁰, D-Arg², Phe(pCl)⁶, Glu⁸,25, D-Lys¹², Ala¹⁵, Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 23

cyclo⁸,12; 21,25 PhAc⁰, D-Arg², Phe(pCl)⁶, Asp⁸, D-Lys¹², Ala¹⁵, Glu²⁵, Nle²⁷ !hGH-RH(1-29)NH₂ Peptide # 24

EXAMPLE IX

Biological Activity

The peptides of the present invention were tested in an in vitro and in vivo assay for their ability to inhibit the hGH-RH(1-29)NH₂ induced GH release.

Superfused Rat Pituitary System. The analogues were tested in vitro in a test described earlier (S. Vigh and A. V. Schally, Peptides 5:241-347, 1984) with modification (Z. Rekasi and A. V. Schally, P. N. A. S. 90:2146-2149, 1993).

Briefly, the cells are preincubated with peptides for 9 minutes (3 mL) at various concentrations. Immediately after the incubation, 1 nM hGH-RH(1-29)NH₂ is administered for 3 minutes (1 mL) 0 minute response!. To check the duration of the antagonistic effect of the analogue, 1 nM hGH-RH(1-29)NH₂ is applied 30, 60, 90, and 120 minutes later for 3 minutes 30, 60, 90, 120 min responses!. Net integral values of the GH responses are evaluated. GH responses are compared to and expressed as percent of the original GH response induced by 1 nM GH-RH(1-29)NH₂. The effect of the new antagonists are compared to that of Ac-Tyr¹,D-Arg² !hGH-RH(1-29)NH₂, the "Standard antagonist".

Growth Hormone Radio-immunoassay. Rat GH levels in aliquots of undiluted and diluted superfusion samples were measured by double-antibody radioimmunoassay using materials supplied by the National Hormone and Pituitary Program, Baltimore, Md. The results of RIA were analyzed with a computer program developed in our institute (V. Csernus and A. V. Schally, Harwood Academic (Greenstein, B. C. ed., London, pp. 71-109, 1991), hereby incorporated by reference. Inter-assay variation was less than 15% and intra-assay variation was less than 10%.

GH-RH Binding Assay. A sensitive radioreceptor binding assay was developed to determine the binding characteristics of the antagonists of GH-RH (G. Halmos, A. V. Schally et al., Receptor 3, 87-97, 1993), hereby incorporated by reference. The assay is based on binding of labelled His¹, Nle²⁷ !hGH-RH(1-32)NH₂ to rat anterior pituitary membrane homogenates. Iodinated derivatives of His¹, Nle²⁷ !hGH-RH(1-32)NH₂ are prepared by the chloramine-T method (F. C. Greenwood et al., Biochemistry 89:114-123, 1963), hereby incorporated by reference. Pituitaries from male Sprague-Dawley rats (250-300 g) are used to prepare crude membranes. For saturation binding analyses, membrane homogenates are incubated with at least 6 concentrations of His¹,125 I-Tyr¹⁰,Nle²⁷ !hGH-RH(1-32)NH₂, ranging from 0.005 to 0.35 nM in the presence or absence of excess unlabelled peptide (1 μM).

The pellet is counted for radioactivity in a γ-counter. The affinities of the antagonist peptides tested to rat pituitary GH-RH receptors are determined in competitive binding experiments. The final binding affinities are estimated by K_(i) (dissociation constant of the inhibitor-receptor complex) and are determined by the Ligand PC computer program of Munson and Rodbard as modified by McPherson. Relative affinities compared to Ac-Tyr¹, D-Arg² !hGH-RH(1-29)NH₂, the Standard antagonist, are calculated as the ratio of K_(i) of the tested GH-RH antagonist to the K_(i) of the Standard antagonist.

In Vivo Tests. Adult male Sprague-Dawley rats are anesthetized with pentobarbital (6 mg/100 g b.w., i.p.). Blood samples are taken from the jugular vein 30 min after the injection of pentobarbital. One group of 7 animals receives hGH-RH(1-29)NH₂ as control. Other groups of rats are injected with Ac-Tyr¹,D-Arg² !hGH-RH(1-29)NH₂ as Standard antagonist, or with one of the antagonist peptide 30 seconds prior to hGH-RH(1-29)NH₂, which is administered at dose of 2-3 μg/kg b.w. Blood samples are taken from the jugular vein 5 and 15 min after the injection of antagonists. GH levels are measured by RIA. Potencies of the antagonists are calculated by the factorial analysis of Bliss and Marks with 95% confidence limits and are based on the doses of 100 and 400 μg/kg b.w. of the Standard antagonist and 20 and 80 μg/kg b.w. of the antagonists tested. Statistical significance was assessed by Duncan's new multiple range test.

Results in vitro. The results of the in vitro antagonistic activities tested in superfused rat pituitary system and binding assay are summarized in Table II and Table lIl, respectively. As can be seen from these data, acylation of the analogs with PhAc or lbu which contain D-Arg² substitution combined with Phe(pCl)⁶ or Nal⁶, Abu⁸, Abu15 or Ala¹⁵, Nle²⁷, Asp²⁸, Agm²⁹ or Arg²⁹ -NH₂, and/or lactam bridge cause an immense increase in receptor binding as well as in inhibition of GH release in vitro and in vivo. Antagonists PhAc⁰, D-Arg², pCl-Phe⁶, Abu¹⁵, Nle²⁷ !hGH-RH(1-28)Agm(MZ-5-156), PhAc⁰ -, D-Arg², Phe(pCl)⁶, Abu⁸,28, Ala¹⁵, Nle²⁷ !hGH-RH(1-29)NH₂ (MZ-5-208), PhAc⁰ -, D-Arg², Phe(pCl)⁶, Abu⁸, Ala¹⁵, Nle²⁷ !hGH-RH(1-29)NH₂ (MZ-5-192), PhAc⁰, D-Arg², Phe(pCl)⁶, Ala¹⁵, Nle²⁷, Asp²⁸ !hGH-RH(1-28)Agm(MZ-5-116), and cyclo 17,21 PhAc⁰, D-Arg², Phe(pCl)⁶, Ser⁸, Ala¹⁵,Glu¹⁷,Nle² !hGH-RH(1-29)NH₂ are the most effective antagonists in vitro.

Results in vivo. Table IV shows the serum GH levels in rats pretreated with GH-RH antagonists. Peptides 7, 8, 9, 11, 13, and 18 produce a significant greater and longer-lasting inhibition of the GH release stimulated by hGH-RH(1-29)NH₂ than the standard antagonist. In vivo experiments, Peptide 8 (MZ-5-156) inhibits hGH-RH(1-29)NH₂ -induced GH-release to greater extent than MZ-4-71, Ibu⁰,D-Arg²,Phe(pCl)⁶,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm, the previously most effective antagonist.

                  TABLE II                                                         ______________________________________                                         Inhibition of GH Release in Superfused Rat Pituitary System                             Dose Inhibition of GH release (%)                                     Peptide    (nM)   0 min  30 min                                                                               60 min                                                                               90 min                                                                               120 min                             ______________________________________                                         Standard antagonist                                                                       100    62.1   2.5   19                                              Peptide 1   3     60.1   12.4  11.5                                                       30     98     49.2  37.6                                            Peptide 2   3     27.4   16.2  48.4  30.2                                                 30     94.7   53.0  24.4  41.8                                      Peptide 3  30     97.4   32.2  35.9  42.1                                      Peptide 4   3     28     21.3  15                                                         30     76.7   53.4  32                                              Peptide 5  30     97.1   93.9  80.1  56.9                                      Peptide 6  30     86.3   89.9  78.9  87.6  62.7                                Peptide 7  30     96.3   41.5  21.5  23.2  20.6                                Peptide 8   3     78.8   73.3  65.9  54.9                                                 10     88.8   83.5  64.9  51.7  42.3                                           30     94.5   90.0  71.5  65.0  55.6                                Peptide 9  30     92.0   80.6  58.9  46.7  46.0                                Peptide 10 30     84.8   35.2  38.2  29.8  33.8                                Peptide 11 30     92.3   80.9  73.3  63.2  55.7                                Peptide 15 30     85.5   65.2  56.1  44.0  46.7                                Peptide 16 30     85.2   12.3  25.1  14.8  36.0                                Peptide 12 30     87.0   61.0  37.0  34.0  41.0                                Peptide 13 30     92.3   90.0  77.3  64.7  61.1                                Peptide 14 30     87.0   32.0   6.0  12.0  24.0                                Peptide 17 30     87.3   46.4  10.7  17.4                                      Peptide 18 30     96.8   79.4  68.3  47.1                                      Peptide 21 30     79.6   56.5  47.5  53.4                                      Peptide 22 30     65.8   37.7  24.9  26.8                                      Peptide 23 30     54.5   28.3  16.3  21.0                                      Peptide 19 30     17.5    0.0  11.2  14.0                                      Peptide 20 30     11.0    0.0   0.0  13.0                                      Peptide 24 30     46.0    6.0  26.0  31.0                                      ______________________________________                                    

                  TABLE III                                                        ______________________________________                                         K.sub.i values and relative affinities (R.A) of hGH-RH antagonists             Peptide       K (nM)        R.A.                                               ______________________________________                                         Standard      3.37 ± 0.14                                                                               1                                                  Peptide 3     0.301 ± 0.14                                                  Peptide 5     0.096         11.19                                              Peptide 8     0.0159 ± 0.01                                                                             35.10                                              Peptide 18    0.159 ± 0.04                                                                              21.19                                              Peptide 11    0.059 ± 0.001                                                                             57.12                                              Peptide 23    0.456          7.39                                              ______________________________________                                    

                  TABLE IV                                                         ______________________________________                                         Serum Growth Hormone Levels in Rats Pretreated with Different                  GH-RH Antagonsists at Different Time Intervals Prior to GH-RH                  (1-29) NH.sub.2 at a Dose of 3 μg/kg                                        Treatment                                                                      Inhibition    Dose     Serum GH Levels                                         (intravenously)                                                                              (μg/kg)                                                                              (ng/mL)      %                                          ______________________________________                                         GH-RH (1-29) NH.sub.2                                                                        3.0      695.15 ± 95.40                                                                            0%                                        Peptide 18                                                                                2 min  80       370.31 ± 48.26                                                                         47%**                                              15 min  80       564.74 ± 76.99                                                                         N.S.                                     Peptide 9  2      80       450.21 ± 68.38                                                                         35%                                      GH-RH (1-29) NH.sub.2                                                                        3.0      703.34 ± 90.01                                                                            0%                                        Peptide 8  2 min  80        177.13 ± 31.75**                                                                      75%                                                15 min  80        183.91 ± 26.19**                                                                      74%                                      GH-RH (1-29) NH.sub.2                                                                        3.0      724.68 ± 93.01                                                                            0%                                        Peptide 8 30 min  80       567.46 ± 50.70                                                                         22% NS                                             60 min  80       582.41 ± 70.18                                                                         20% NS                                   GH-RH (1-29) NH.sub.2                                                                        3.0       883.36 ± 148.34                                                                          0%                                        Peptide 13                                                                                2 min  80        316.01 ± 68.24**                                                                      64%                                                15 min  80        641.73 ± 92.01*                                                                       27%                                      GH-RH (1-29) NH.sub.2                                                                        3.0      703.34 ± 93.01                                                                            0%                                        Peptide 7  2 min  80        611.07 ± 87.75*                                                                       31%                                                15 min  80        688.39 ± 107.91                                                                       N.S.                                     GH-RH (1-29) NH.sub.2                                                                        3.0      724.68 ± 93.01                                                                            0%                                        Peptide A 15 min  80        585.33 ± 89.34*                                                                       43%                                                30 min  80       788.39 ± 96.93                                                                         23% NS                                   ______________________________________                                          Data are expressed as mean ± SEM                                            *p < 0.05 vs control                                                           **p < 0.01 vs control                                                          NS not significant                                                       

Effect of GH RH antagonists on SW 1990 human pancreatic cancers in nude mice

Small piees of an SW-1990 rumor growing in a nude mouse were transplated s.c. into the right flanks of 60 nu/nu male nude mice. Ten days after transplantation, 40 mice with well growing tumors were groupled into 4 groups with equal average tumor volume (16 mm³) in each group. Treatment started 13 days after transplantation and was continuted for 44 days. Groups are shown in the table. The tumors were measured and volume was calculated weekly. Tumor volume changes are shown in Table V. On day 45 of treatment the mice were sacraficed under Metofane anesthesia by exsanguination from abdominal aorta. Blood was collected, tumor and organ weights were determined.

Histology, receptor studies and determination of blood hormone levels are in progress.

Results

Tumor volume data and tumor weights at the end of the experiment are shown in the table. Treatment with 10 μg/day of Peptide #8 resulted in a significant inhibition of growth of SW-1990 cancers as shown by volume and weigth data. Peptide A had no significant effect on the tumors. Body, liver, kidney and spleen weights showed no significant differences from control values.

Effect of treatment with GH-RH antagonists on tumor weights and final tumor volume of SW-1990 humane pancreatic cancers growing in nude mice.

                  TABLE V                                                          ______________________________________                                         Group          Dose    Number of                                                                             Tumor   Final Tumor                              No.   Treatment                                                                               mg/day  mice   weights (mg)                                                                           Volume mm.sup.3                          ______________________________________                                         1     Control          10     1467 ± 374                                                                          1291 ± 301                            2     Peptide A                                                                               10      10     1467 ± 595                                                                          1183 ± 342                            3     Peptide A                                                                               40      10     1297 ± 258                                                                           902 ± 156                            4     Peptide B                                                                               10      10      931 ± 330                                                                           612 ± 220*                           ______________________________________                                          *p < 0.05                                                                      Peptide A: Ibu.sup.0 --D--Arg.sup.2 --Phe(pCl).sup.6 --Abu.sup.16              --Nle.sup.27 ! hGHRH (1-28) Agm                                          

    __________________________________________________________________________     #             SEQUENCE LISTING                                                 - (1) GENERAL INFORMATION:                                                     -    (iii) NUMBER OF SEQUENCES: 1                                              - (2) INFORMATION FOR SEQ ID NO:1:                                             -      (i) SEQUENCE CHARACTERISTICS:                                                     (A) LENGTH: 29                                                                 (B) TYPE:Amino                                                                 (C) STRANDEDNESS:Unknown                                                       (D) TOPOLOGY:Unknown                                                 -     (ii) MOLECULE TYPE: peptide                                              -     (ix) FEATURE:                                                            #A lactam bridge is INFORMATION:                                                              formed be - #tween any one of the pairs of positions                           1,2; 2,3; - #8,12; 16,20; 17-21; 21,25; 25,29 or both           #21,25 positions.12 and                                                                       X  att - #ached to position 1 is  H, Ac, Aqc, IAc,                             BrProp, F - #or, Ibu, Nac, 2-Nac, 1- or 2-Npt, 1- or                           2-Npr, Ph - #Ac, Fpr, or any other aromatic or                  #acyl group,   nonpolar                                                        #Glu,          Xaa1 is                                                                        Gln, Asp, - # Asn, Abu, Leu, Tyr, His,Phe(Y), in                               which Y=- #H, F, Cl, Br, NO2, NH2, CH3 or OCH3 as a             #in the phenyl ring thereof, Ser, Thr,                                                        Val, Ile, - # Ala, Abu, Nle, or Aib,                            #Lys, Arg, Orn, or Agmatine,                                                   #Glu,          Xaa3 is                                                                        Gln, Asp, - # Asn, Abu, Leu, Tyr, His, Phe(Y), in                              which Y=- #H, F, Cl, Br, NO2, NH2, CH3 or OCH3 as a             #in the phenyl ring thereof, Ser, Thr,                                                        Val, Ile, - # Ala, Abu, Nle, or Aib,                            #Ala, Abu or Gly,a4 is                                                         #Ile, Ala or Gly,a5 is                                                         #Phe, 1,2,3,4,-tetrahydrisoquinoline,                                                         2,3,4,9-tetr - #ahydro-1H-pyrido 3,4-b!indol-3-                 #acid, 2-naphthylalanine or Phe(Y), in                                                        which Y=- #H, F, Cl, Br, NO2, NH2, CH3 or OCH3, as a            #in the phenyl ring thereof,                                                   #Glu,          Xaa8 is                                                                        Gln, Asp, - # Asn, Abu, Leu, Tyr, His, Phe(Y), in                              which Y=- #H, F, Cl, Br, NO2, NH2, CH3 or OCH3 as a             #in the phenyl ring thereof, Ser, Thr,                                                        Val, Ile, - # Ala, Abu, Nle, or Aib,                            #Tyr or Phe(Y), in which Y=H, F, Cl, Br,                                                      NO2, NH2, - # CH3 or OCH3, as a substituent in the                             phenyl ri - #ng thereof,                                        #Arg or 2-amino-5-ureidovaleric acid                                           #Lys, Arg, Orn, or Agmatine,                                                   #Gly, Ala, Abu or Gln,s                                                        #Glu,          Xaa16 is                                                                       Gln, Asp, - # Asn, Abu, Leu, Tyr, His, Phe(Y), in                              which Y=- #H, F, Cl, Br, NO2, NH2, CH3 or OCH3 as a             #in the phenyl ring thereof, Ser, Thr,                                                        Val, Ile, - # Ala, Abu, Nle, or Aib,                            #is Glu,       Xaa17                                                                          Gln, Asp, - # Asn, Abu, Leu, Tyr, His, Phe(Y), in                              which Y=- #H, F, Cl, Br, NO2, NH2, CH3 or OCH3 as a             #in the phenyl ring thereof, Ser, Thr,                                                        Val, Ile, - # Ala, Abu, Nle, or Aib,                            #Ala or Abu,   Xaa19 is                                                        #Lys, Arg, Orn, or Agmatine,                                                   #Lys, Arg, Orn, or Agmatine,                                                   #is Glu,       Xaa25                                                                          Gln, Asp, - # Asn, Abu, Leu, Tyr, His, Phe(Y), in                              which Y=- #H, F, Cl, Br, NO2, NH2, CH3 or OCH3 as a             #in the phenyl ring thereof, Ser, Thr,                                                        Val, Ile, - # Ala, Abu, Nle, or Aib,                            #Met, Nle or Abu,a27 is                                                        #Ser, Asn, Asp, Ala or Abu,                                                    #Lys, Arg, Orn, or Agmatine.                                                   #1:   (xi) SEQUENCE DESCRIPTION: SEQ ID NO:                                    - Xaa Xaa Xaa Xaa Xaa Xaa Thr Xaa Ser Xaa Xa - #a                              #                 10                                                           - Xaa Val Leu Xaa Xaa Xaa Ser Xaa Xaa Xaa Le - #u                              #             20                                                               - Leu Gln Xaa Ile Xaa Xaa Xaa                                                          25                                                                     __________________________________________________________________________ 

We claim:
 1. A compound having the formula Ibu⁰,D-Arg²,Phe(pCl)⁸,10,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm.
 2. A compound of having the formula PhAc⁰,D-Arg²,Phe(pCl)⁸,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm.
 3. A compound having the formula PhAc⁰,D-Arg², Phe(pCl)⁶,Abu⁸,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)NH₂.
 4. A compound having the formula PhAc⁰,D-Arg²,Phe(pCl)⁶,Abu⁸,28,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂.
 5. A compound of claim 1 selected from the group consisting ofcyclo⁸,12 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂, cyclo¹⁷,21 PhAc⁰,D-Arg²,Phe(pCl)⁶,Ser⁸,Ala¹⁵,Glu¹⁷,Nle²⁷ !hGH-RH(1-29)-NH₂, cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,25,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm, cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,D-Asp³,Phe(pCl)⁶,Glu⁸,25,D-lys.sup.12,Ala ¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂, and cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,25 ,D-Lys ¹²,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂.
 6. A compound of claim 5 having the formula cyclo⁸,12 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂.
 7. A compound of claim 5 having the formula cyclo¹⁷,21 PhAc⁰,D-Arg²,Phe(pCl)⁶,Ser⁸,Ala¹⁵,Glu¹⁷,Nle²⁷ !hGH-RH(1-29)-NH₂.
 8. A compound of claim 5 having the formula cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,25,Abu¹⁵,Nle²⁷ !hGH-RH(1-28)Agm.
 9. A compound of claim 5 having the formula cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,D-Asp³,Phe(pCl)⁶,Glu⁸,25,D-Lys.sup.12,Ala¹⁵,Nle²⁷ !hGH-RH(1-29)-NH₂.
 10. A compound of claim 5 having the formula cyclo⁸,12; 21,25 PhAc⁰,D-Arg²,Phe(pCl)⁶,Glu⁸,25,D-Lys¹²,Ala.sup.15,Nle²⁷ !hGH-RH(1-29)-NH₂.
 11. A method of suppressing excessive levels of GH in a patient in need of same which comprises administering said patient an effective amount of a compound in accordance with claim
 5. 12. A method of claim 11 wherein the patient is a patient having a cancer carrying receptors for IGF-I.
 13. A method of suppressing excessive levels of GH in a patient in need of same which comprises administering said patient an effective amount of a compound of claim
 1. 14. A method of claim 13 wherein the patient is a patient having a cancer carrying receptors for IGF-I.
 15. A method of suppressing excessive levels of GH in a patient in need of same which comprises administering said patient an effective amount of a compound of claim
 2. 16. A method of claim 15 wherein the patient is a patient having a cancer carrying receptors for IGF-I.
 17. A method of suppressing excessive levels of GH in a patient in need of same which comprises administering said patient an effective amount of a compound of claim
 3. 18. A method of claim 17 wherein the patient is a patient having a cancer carrying receptors for IGF-I.
 19. A method of suppressing excessive levels of GH in a patient in need of same which comprises administering said patient an effective amount of a compound of claim
 4. 20. A method of claim 19 wherein the patient is a patient having a cancer carrying receptors for IGF-I. 